1. Field of the Invention
This invention is directed to a seismically qualified termination frame assembly for mounting electronic circuit boards such as signal conditioner circuit boards for data acquisition systems and for providing protection of the circuit board input and/or output signals from surges and from electromagnetic interference (EMI) generated by noise on the field wiring to which the input and output circuits on the boards are connected. The invention further encompasses apparatus which mounts a plurality of such assemblies with all of the field wiring accessible from one side of an EMI barrier and the circuit boards accessible from the other side, and which incorporates busses for supplying power, test signals and a common ground to the boards through plug-in connections.
2. Prior Art
Present day electronic data acquisition systems commonly use microprocessors mounted on printed circuit boards to manage data input and output. The industrial grade printed wiring boards typically used are extremely sensitive to noise, and to electromagnetic, including radio frequency, interference. In addition, the various field signals are often referenced to a high common mode voltage and are susceptible to line surges. In order to combat these difficulties, a family of front-end printed circuit signal conditioner boards is used to provide the required system immunity.
Another problem encountered in such data acquisition systems is that the field wiring, such as for instance, neoprene jacketed AWG #16 shielded pair cabling which measures 3/8 inch in diameter, is not compatible in size with the edge connectors used to interface with the densely packed terminations on the computer input/output boards. This requires intermediate wiring between the field wiring and the card edge connectors.
In the typical data acquisition system, the field wiring is terminated on a barrier strip in a cabinet housing the microprocessor. The signal conditioning circuitry is located either in the computer chassis or in a separate card cage mounted nearby. This packaging approach allows electrical noise coming into the cabinet on the field wiring to exist inside the cabinet in close proximity to the sensitive unprotected electronics and thereby defeats the use of the protective signal conditioning circuits.